$ git clone -n https://src.fedoraproject.org/rpms/root.git /var/lib/mock/f40-build-763322-122469/root/chroot_tmpdir/scmroot/root
Cloning into '/var/lib/mock/f40-build-763322-122469/root/chroot_tmpdir/scmroot/root'...
$ git fetch origin 6d457ab71f59f244f20986dd144dec499ca8dfc1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/root
 * [new ref]         6d457ab71f59f244f20986dd144dec499ca8dfc1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6d457ab Update to 6.30.02